Immobilization of phospholipids on silicon, platinum, indium/tin oxide and gold surfaces with characterization by x-ray photoelectron spectroscopy and time-of-flight secondary-ion mass spectrometry

Abstract Simple procedures are described for the covalent binding of phospholipids to silicon, platinum, indium/tin oxide and gold surfaces. The protocol for the first three surfaces consists of silanization with γ-amino propyltriethoxysilane, followed by reaction of the amino function with a derivative of a long-chain aliphatic dicarboxylic acid used as a cross-linker and treatment with a lyso-lipid. The seposition of a lipid on gold emplys the reactivity of a sulphur substituent at the terminus on one of the acyl chains of the lipid. Surface coverages ranging from 60 to 75% are obtained as deduced from elemtnal determinations and N(1 s )-to-P(2 p binding energy peak ratios obtained in x-ray photoelectron spectroscopic study of the immobilized species. Functional group determinations were done through a high-resolutions of the C(1 s peaks together with comparison of spectra from intermediate surface structures. Depth profiling of the lipid-bound silicon surface through argon ion etching indicated a model involving the orientation of the sn -2 chain perpendicular to the surface plane. The molecular structure of the immobilized lipid on silicon is established by positive and negative time-of-flight secondary-ion mass spectrometry.